NEW YORK (CNN) -- Nonnie Dotson, a nurse in the U.S. Air Force, was decompressing from a hard-fought child support battle when she disappeared hundreds of miles from her home base.

Dotson, 33, was staying with her brother at his home outside Denver, Colorado, when she vanished on November 19, 2006. She was supposed to meet friends at the mall for a smoothie.

She never showed.

The single mother and her 16-month-old daughter, Savannah, lived in San Antonio, Texas, where Dotson worked on a military base as an intensive care nurse. They were staying with Dotson's brother, Tony, for a few days. Watch why Dotson's disappearance puzzles investigators

Dotson had recently emerged from a court battle with Ed Vehle, Savannah's father. Vehle, who also lived in San Antonio, was ordered by the court to pay $10,000 in back child support, as well as $900 each month. Dotson won the court order two months before she disappeared.

Dotson was just months away from completing her military duty and was trying to decide whether she would move back to her hometown in Colorado or remain in San Antonio.

Vehle had declared he had no interest in being a part of their lives. The two met in 2004 and the relationship ended when Dotson became pregnant. Vehle did not want her to have the baby, she told friends at the military base. The friends spoke on condition that their identities would not be made public. Vehle is not a suspect or person of interest in the case, police said.

Because things appeared to be going well in Dotson's life, her sudden disappearance is a mystery to her family and to police. She was hundreds of miles away from home in a safe Denver suburb. She left her brother's home on Sunday afternoon, and the mall was within walking distance,Tony Dotson said.

"She asked me to look after Savannah for a couple hours and she walked out that door and we never saw her again," Tony Dotson added. "She would never have intentionally left Savannah behind like that." Police agree.

Since Dotson vanished, there has been no activity on her bank accounts, credit cards or cell phone, police said. Her case is still an open missing persons investigation being handled by the Jefferson County homicide department.

"Unfortunately, we have no real leads as to who is responsible for Dotson's disappearance," said sheriff's office spokeswoman Jacki Kelley.

"She could be alive and being held against her will. She could have been kidnapped and then murdered. We are not ruling anything out at this time," Kelley said.

For several weeks after Dotson's disappearance, Vehle refused to answer questions. He retained counsel. In mid-December 2006, Vehle and Jay Norton, his attorney, met with police, answering all their questions.

Norton said they were able to provide investigators with receipts and cell phone records accounting for Vehle's whereabouts. Police confirmed that Vehle was nowhere near Colorado before, during or after Dotson's disappearance.

After Dotson's disappearance, Vehle decided to go to court to pursue full custody of his daughter. Dotson's parents had been taking care of Savannah. The court last year gave Vehle shared custody with Dotson's parents.

Family and police urge anyone with information about the whereabouts of Nonnie Dotson to call the Jefferson County Sheriff's Office tip line at (303) 271-5612. Nonnie Dotson is 5 feet 3 inches tall, weighs 115 pounds and has brown hair and brown eyes.